1. High Dk Ophthalmic Moldings
In the field of ophthalmic moldings, and in particular in the field of contact lenses, a biocompatible lens may be generally defined as one which will not substantially damage the surrounding ocular tissue and ocular fluid during the time period of contact. The phrase “ophthalmically compatible” more appropriately describes the biocompatibility requirements of ophthalmic lenses.
One ophthalmic compatibility requirement for contact lenses is that the lens must allow oxygen to reach the cornea in an amount which is sufficient for long-term corneal health. The contact lens must allow oxygen from the surrounding air to reach the cornea because the cornea does not receive oxygen from the blood supply like other tissue. If sufficient oxygen does not reach the cornea, corneal swelling occurs. Extended periods of oxygen deprivation causes the undesirable growth of blood vessels in the cornea. “Soft” contact lenses conform closely to the shape of the eye, so oxygen cannot easily circumvent the lens. Thus, soft contact lenses must allow oxygen to diffuse through the lens to reach the cornea.
While there exist rigid gas permeable (“RGP”) contact lenses which have high oxygen permeability and which move on the eye, RGP lenses are typically quite uncomfortable for the consumer. Thus, soft contact lenses are preferred by many consumers because of comfort. Moreover, a contact lens which may be continuously worn for a period of a day or more (including wear during periods of sleeping) requires comfort levels which exclude RGP lenses as popular extended-wear candidates.
In order to balance the ophthalmic compatibility and consumer comfort requirements in designing a daily wear soft contact lens, polymers and copolymers of 2-hydroxyethyl methacrylate (HEMA) were developed. These hydrophilic polymers move well on the eye and provide sufficient oxygen permeability for daily wear. Certain soft contact lenses have been approved by the FDA for extended wear periods of up to about 6 nights of overnight wear and seven days of daily wear. However, the consumer cannot safely and comfortably wear these poly(HEMA) lenses for extended periods of seven days or more, because the oxygen permeability is insufficient. True extended wear (i.e., seven days or more) of these lenses may result, at a minimum, in corneal swelling and development of surface blood vessels in the cornea.
In order to improve oxygen permeability, polymers containing silicone groups were developed. A variety of siloxane-containing polymers have been disclosed as having high oxygen permeability (high Dk). For example, see U.S. Pat. Nos. 3,228,741; 3,341,490; 3,996,187; and 3,996,189.
2. Tinted Ophthalmic Moldings
A number of dyes have been incorporated into ophthalmic moldings, such as contact lenses, for a variety of reasons. Two popular type of dyes include ultraviolet (UV) light absorbing agents. One common reason for incorporating dyes into contact lenses is to produce a lens that changes the apparent perceived color of the wearer's iris. Another reason to dye a lens is to enable the user to easily locate a lens in a clear solution within a lens storage, disinfecting or cleaning container. Dyeing a lens for this purpose is for “visibility tinting” the lens.
Visibility tinting may be accomplished by applying a dye to a portion of the surface or by applying the dye to the full front surface of the lens. Alternatively, the tint may be incorporated into the full body of the polymer matrix of the lens. There have been a number of patents and published patent applications relating to tinting contact lenses or making contact lenses that change the wearer's iris color. However, these processes are not yet totally satisfactory, for example, with respect to the types of lens materials used to tint, the production efficiency, and/or the quality of the products obtained.
Thus, there remains a need for an ophthalmically compatible, visibility tinted transparent polymeric lens material which is suited to short and extended periods of continuous contact with ocular tissue and tear fluid. In addition, there is still a need for a method of making an improved visibility tinted, i.e., a full body, edge-to-edge tinted contact lens with an improved efficiency by minimizing in-line production steps. Also, there remains a need for a method for tinting or coloring a lens that does not require the use of reactive dyes and associated wet processing necessary to remove unbound dye, activator and reaction by-products.
Moreover, there is a need for tinted ophthalmic lenses with improved properties, for example, with respect to high oxygen permeability, increased mechanical strength, reduced leaching or migration of dye or pigment out of the lens material and color retention during exposure to UV light during photopolymerization.